For power supply and distribution to multiple computers and servers in a data center, a conventional power distribution unit (PDU) is utilized to distribute electric power. Depending on the area or the country where the data center is located, specification of the mains electricity provided to the data center may vary. Therefore, the conventional PDU is designed according to the specification of the mains electricity. For example, the mains electricity in North America is three-phase electric power, using five-wire outlets to provide a line-to-neutral voltage of 120 V and a line-to-line voltage of 208 V.
However, the conventional PDU is limited to outputting electricity through its sockets in only one of the following three configurations: (1) with all of the sockets outputting the line-to-neutral voltage, (2) with all of the sockets outputting the line-to-line voltage, and (3) with a fixed number of the sockets outputting the line-to-neutral voltage and the remaining sockets outputting the line-to-line voltage. Namely, each of the sockets of the conventional PDU can output either the line-to-line voltage or the line-to-neutral voltage. In the case of a data center where most of the computers require the line-to-neutral voltage and only a few require the line-to-line voltage, either the conventional PDUs with configurations (1) and (2), or only the conventional PDUs with the configuration (3) can be used. Unfortunately, in this way, usage of the conventional PDU(s) is inefficient because most of the sockets outputting the line-to-line voltage would not be utilized.